Priced a exmark lazer z hp 50 with a 23 kaw and a 52 as with a 28 kaw. How much harder on fuel would the 28 be over the 23. Also was looking at the hp 46 with a 19. I would guess that the 19 would be the best on fuel but not sure. I want something around a 50" cut because of the size yards I mow.